As you maintain your server, your list of installed packages will grow. If, for some reason, you needed to rebuild your server, you would need to reproduce exactly what you had installed before, which can be a pain. It's always recommended that you document all changes made to your server via a change control process, but, at the very least, keeping track of which packages are installed is an absolute must. In some cases, a server may only include one or two extra packages in order to meet its goal, but, in other cases, you may need an exact combination of software and libraries in order to get things working. Thankfully, the dpkg command allows us to export and import a list of packages to install.
To export a list of installed packages, we can use the following command:
dpkg –get-selections > packages.list
This command will dump a list of package selections to a standard text file. If you open it, you'll see a list of your installed packages, one per...